This load weighing system provides a solution to elevator load weighing problems. The control/sensor provides feedback pertaining to the load in the elevator cab.
Most elevators are housed in a cage. The cab of the elevator rests on springs at the bottom of the cage structure. As the in cabin load of the elevator increases, the springs compress. The distance from the top to the cage (which is fixed) to the top of the elevator increases as the load in the elevator increases. A system needs to account for the elevator actually becoming heavier as it travels up the shaft. Elevators have trailing cables and as the elevator rises, a system needs to compensate for the additional weight.
Another factor is knowing when the doors are open or closed. If the doors are open, the weight data is allowed to change, since elevators are not allowed to move with the doors open. If the doors are closed, the last weight that was captured with the doors open is held. Once the doors close, the weight will not change and acceleration of the elevator could throw the reading off.
Other controls take information from this load sensing board. The motor control might use the information to determine how much power is needed for take off torque. The elevator control may stop the elevator if the load is too great. Also, if the elevator is somewhat full and is traveling, the control may decide to dispatch other elevators to incoming calls instead of having a full elevator stop and service the call.
This design provides an elegant solution to elevator load weighing applications. The purpose of this control is to provide meaningful feedback pertaining to the load that is in the elevator cab. This system can accept any one of four different types of sensor for determining cab displacement. A linear potentionmeter, LVDT, or proximity sensor may be used with this system. Load feedback is provided by these different mechanisms. Five relays are provided and may be programmed to turn ON and OFF at user defined loads. A current loop is available to transmit load information. The loop is set to 4 mA when the load is zero. A 20 mA value is a user-definable value that can be set to any value up to 200% of the maximum elevator load. Serial information is also available. The serial port may be set up to constantly transmit load information over the serial link. The system may receive information pertaining to floor, door position, and direction through MICRO COMM(copyright) link or through discreet optically isolated inputs. The opto-isolators can be configured to handle AC or DC voltages in many ranges. MICRO COMM(copyright) is a registered trademark for elevator controls and floor indicators.